fix: Remove unused import

Author: diegomarquezp

oauth2_http/javatests/com/google/auth/oauth2/GdchCredentialsTest.java

@@ -54,7 +54,6 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
-import java.lang.reflect.Method;
 import java.net.URI;
 import java.nio.file.Files;
 import java.security.KeyPair;